• 제목/요약/키워드: Strain-based

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티타늄 합금의 변형률속도 및 온도를 고려한 인공신경망 기반 경화모델 성능평가 (Evaluation of Performance of Artificial Neural Network based Hardening Model for Titanium Alloy Considering Strain Rate and Temperature)

  • 김민기;임성식;김용배
    • 소성∙가공
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    • 제33권2호
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    • pp.96-102
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    • 2024
  • This study addresses evaluation of performance of hardening model for a titanium alloy (Ti6Al4V) based on the artificial neural network (ANN) regarding the strain rate and the temperature. Uniaxial compression tests were carried out at different strain rates from 0.001 /s to 10 /s and temperatures from 575 ℃ To 975 ℃. Using the experimental data, ANN models were trained and tested with different hyperparameters, such as size of hidden layer and optimizer. The input features were determined with the equivalent plastic strain, strain rate, and temperature while the output value was set to the equivalent stress. When the number of data is sufficient with a smooth tendency, both the Bayesian regulation (BR) and the Levenberg-Marquardt (LM) show good performance to predict the flow behavior. However, only BR algorithm shows a predictability when the number of data is insufficient. Furthermore, a proper size of the hidden layer must be confirmed to describe the behavior with the limited number of the data.

Karasek의 Job Content Questionnaire와 Korea Occupational Stress Scale의 비교 연구 (Comparison of Karasek's Job Content Questionnaire and Korea Occupational Stress Scale)

  • 이종빈;장성록
    • 한국안전학회지
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    • 제30권1호
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    • pp.72-78
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    • 2015
  • According to the report of the WHO, workers have been exposed to much job strain such as job load, responsibility, role, interpersonal conflict etc. In Korea, studies on job strain started to become active from 1990s and now hundreds of studies are actively under going or publishing so that the studies are contributing to development and improvement of job strain. Representative measurement models of job strain are Job Strain Model of Karasek, Job Stress Model of NOISH, Korea Occupational Stress Scale, JSQ(Job Stress Questionnaire), K-OSI(Korea Version of Occupational Stress Inventory) etc. (Lee Kwan-Suk, 2012 ; KOSHA, 2003). Among them, Job Strain Model of Karasek had been loved by many researchers of job strain before Korea Occupational Stress Scale was developed. Job Strain Model of Karasek had been fitted to Korean style and then, used to analyze job strain of Korean people so that this Scale highly contributed to seeking relationship with cardiovascular disease, musculoskeletal disease caused by job, smoking, drug, alcohol poisoning, and pulse(Lee Kwan-Suk, 2012). But as this Model was studied and developed based on foreign culture and life pattern, a model fit to Korea was developed to measure job strain for Korean people, which is Korea Occupational Stress Scale now most frequently used in measuring job strain. Accordingly, after this study made questionnaire survey about same population using the two methods used most frequently in measuring job strain, the study investigated what features appeared, what correlations appear between two models, and comparatively analyzed characteristics each independent and dependent variable. Based on this, the study aimed to exactly express job strain of Korean people. The subjects of the study were a population of 233, and Karasek's Questionnaire and KOSS's Questionnaire were surveyed at the same time. The results were analyzed by statistical program to obtain significant difference between two models. Four particular groups were divided with Job Strain Model of Karasek and the four particular groups were measured with Korea Occupational Stress Scale. And job strain come from combination of two models was measured, with which new comparative analysis method was suggested.

금속재료 응력-변형률 곡선의 수학적 표현들 (Mathematical Expressions for Stress-Strain Curve of Metallic Material)

  • 현홍철;이진행;이형일
    • 대한기계학회논문집A
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    • 제32권1호
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    • pp.21-28
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    • 2008
  • 본 연구에서는 인장과 압축실험 데이터를 사용하여 재료의 응력-변형률 곡선을 얻었다. 시편에 네킹 현상이 발생하기 전에는 인장실험의 결과를 토대로 각 재료의 영률값과 항복강도를 찾았다. 이후 비선형 거동은 압축실험의 데이터를 이용해 나타냈다. 이렇게 얻어진 재료의 실제응력-변형률 곡선을 구간 멱함수법을 사용해 변형률 구간별로 회귀하였다. 회귀하여 구한 곡선과 실제 재료의 응력-변형률 곡선을 비교해 최적 회귀방법과 상응하는 변형률 회귀구간을 찾았다. 하나와 두 변수에 의한 회귀를 혼용하면 가장 적절한 회귀 방법이 얻어진다. 우선 두 변수들로 회귀하여 항복강도를 찾는다. 뤼더변형률이 없는 재료의 항복강도를 예측에는 초기구간 데이터만을 이용해야 오차를 최소화 할 수 있다. 한편 뤼더변형률이 재료들은 곡선의 후반부 데이터를 사용해야 정확한 물성치를 찾아낼 수 있다. 이어 항복 강도가 구해진 상황에서 응력-변형률 곡선의 전체 데이터를 사용해, n을 단일변수로 하여 회귀한다. 여기서 얻은 항복강도와 n을 이용하면 실제 실험 응력-변형률 곡선을 가장 유사하게 따라가는 회귀곡선을 얻을 수 있다.

신축성 금속 나노선 압저항 전극 기반 로젯 스트레인 센서 (Rosette Strain Sensors Based on Stretchable Metal Nanowire Piezoresistive Electrodes)

  • 김강현;차재경;김종만
    • 대한금속재료학회지
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    • 제56권11호
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    • pp.835-843
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    • 2018
  • In this work, we report a delta rosette strain sensor based on highly stretchable silver nanowire (AgNW) percolation piezoresistors. The proposed rosette strain sensors were easily prepared by a facile two-step fabrication route. First, three identical AgNW piezoresistive electrodes were patterned in a simple and precise manner on a donor film using a solution-processed drop-coating of the AgNWs in conjunction with a tape-type shadow mask. The patterned AgNW electrodes were then entirely transferred to an elastomeric substrate while embedding them in the polymer matrix. The fabricated stretchable AgNW piezoresistors could be operated at up to 20% strain without electrical or mechanical failure, showing a maximum gauge factor as high as 5.3, low hysteresis, and high linearity ($r^2{\approx}0.996$). Moreover, the sensor responses were also found to be highly stable and reversible even under repeated strain loading/unloading for up to 1000 cycles at a maximum tensile strain of 20%, mainly due to the mechanical stability of the AgNW/elastomer composites. In addition, both the magnitude and direction of the principal strain could be precisely characterized by configuring three identical AgNW piezoresistors in a delta rosette form, representing the potential for employing the devices as a multidimensional strain sensor in various practical applications.

Anchor 볼트 형태의 Strain Gauge 센서를 이용한 지게차 적재 중량 측정 시스템 (Forklift Weight Measurement System using Anchor Bolt Type Strain Gauge Sensor)

  • 한치문;임춘식;이성렬
    • 한국항행학회논문지
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    • 제23권2호
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    • pp.200-206
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    • 2019
  • 산업현장에서의 지게차의 전복에 의한 안전사고 빈도가 매우 높은 편이다. 지게차 전복의 가장 큰 원인은 과적으로, 이를 방지하기 위해서 적재 중량을 측정해야 한다. 가장 보편적인 적재 중량 측정 방식은 로드셀(load cell)로 측정 오차가 적은 장점이 있지만 설치 단가가 비싸다는 점 때문에 산업현장에 쉽게 적용하지 못하고 있다. 본 연구는 로드 셀 방식의 대안으로 제시되었지만 측량 정밀도가 높지 않은 strain gauge 센싱 방식을 적용한 지게차 새로운 적재 중량 측정 시스템을 제안한다. 센서의 측량 정밀도와 내구성을 높이기 위해 4개의 센서가 각각 4개의 anchor bolt에 삽입되는 구조로 제작하였다. 제작된 anchor 볼트 형태의 strain gauge 센서를 지게차에 적용하여 측정한 결과 1%의 측정 오차를 얻을 수 있었다.

Viscoelastic constitutive modeling of asphalt concrete with growing damage

  • Lee, Hyun-Jong;Kim, Y. Richard;Kim, Sun-Hoon
    • Structural Engineering and Mechanics
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    • 제7권2호
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    • pp.225-240
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    • 1999
  • This paper presents a mechanistic approach to uniaxial viscoelastic constitutive modeling of asphalt concrete that accounts for damage evolution under cyclic loading conditions. An elasticviscoelastic correspondence principle in terms of pseudo variables is applied to separately evaluate viscoelasticity and time-dependent damage growth in asphalt concrete. The time-dependent damage growth in asphalt concrete is modeled by using a damage parameter based on a generalization of microcrack growth law. Internal state variables that describe the hysteretic behavior of asphalt concrete are determined. A constitutive equation in terms of stress and pseudo strain is first established for controlled-strain mode and then transformed to a controlled-stress constitutive equation by simply replacing physical stress and pseudo strain with pseudo stress and physical strain. Tensile uniaxial fatigue tests are performed under the controlled-strain mode to determine model parameters. The constitutive equations in terms of pseudo strain and pseudo stress satisfactorily predict the constitutive behavior of asphalt concrete all the way up to failure under controlled-strain and -stress modes, respectively.

Real-Time Observation of Temperature-Dependen Strain in Poly (3-hexylthiophene) Crystals in a Mixed Donor and Acceptor Thin Film

  • 이현휘;김효정
    • 한국진공학회:학술대회논문집
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    • 한국진공학회 2012년도 제43회 하계 정기 학술대회 초록집
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    • pp.163-163
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    • 2012
  • We observed strain evolution of P3HT crystals in P3HT:PCBM films and the effect of Al electrode on the evolution during real time annealing process. Based on simple assumptions, both relaxed lattice parameters and thermal expansion coefficient could be quantitatively determined. P3HT:PCBM films displayed tensile strain in as-prepared samples regardless of the presence of an Al layer. In the absence of Al layer, P3HT crystals showed only strain relaxation at an annealing temperature of $180^{\circ}C$. Meanwhile In the presence of an Al layer, the strain was relaxed and changed to compressive strain at around 120C annealing temperature, which indicated a tightening of the thiophene ring packing. These behaviors support the improved performance of devices fabricated by post annealing process.

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유동응력의 비선형 속도 민감도에 대한 모델링 (Modeling on the Nonlinear Rate Sensitivity of Flow Stress)

  • 호광수
    • 대한기계학회논문집A
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    • 제28권6호
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    • pp.670-676
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    • 2004
  • Most metallic materials and alloys show rate independence or negative rate sensitivity in some temperature region when dynamic strain aging occurs. It is generally recognized that negative rate sensitivity is an essential feature of dynamic strain aging that can depend on strain and/or strain rate. The unified viscoplasticity theory based on overstress is applied to reproduce a change of rate sensitivity type that depends on strain or strain rate. This is accomplished through the introduction of a single new term in the growth law of the equilibrium stress, which is a tensor valued state variable of the model. It is also shown that the new term can be used to reproduce a dramatic increase of rate sensitivity in dynamic plasticity.

수용성 청색색소를 생산하는 Azotobacter vinelandii A80 균주의 분리 및 특성 (Isolation and characterization of Azotobacter vinelandii Strain A80 Producing Water-soluble Blue Pigment)

  • 배수장;김광현;김병우;김영희
    • 한국미생물·생명공학회지
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    • 제23권1호
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    • pp.43-46
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    • 1995
  • For using additives of foods, or cosmetics, a strain A80 producing blue pigment was isolated from soil. The strain A80 was identified as a strain of Azotobacter vinelandii based on morphological and physiological characteristics. The strain A80 was extracellulaly secreted the blue pigment on PYG agar plate, but not secreted it into PYG broth. And then, the strain A80 was extracellulaly secreted the blue pigment in PYG broth containing 2.0% chitin, while the strain A80 was not secreted the blue pigment in PYG broth containing 2.0% chitin and 1% NaCl simultaniously.

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해양에서 용균효소를 분비하는 균주의 분리와 동정 (Isolation and Identification of a Bacteriolytic Enzyme-producing Bacterial Strain from Pusan Coastal Sea)

  • 진성현;류병호
    • 한국미생물·생명공학회지
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    • 제23권5호
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    • pp.580-587
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    • 1995
  • In order to produce the bacteriolytic enzyme, bacterial strains capable of excreting a large amount of the enzyme were screened from the coastal sea water samples in Pusan. The bacterial strain SH-1, which showed the highest activity among 43 bacteriolytic enzyme producing bacteria, was finally selected for further studies. The strain SH-1 was an endospore-forming grampositive rod, and the position of spore was paracentral. These morphological characteristics assigned the isolated strain to the morphological group I classified by Gordon. The fatty acid composition of the bacterial stain was analyzed to be consisted of branched chains of iso-Cn and anteiso-Cn. Based on the percent content of the branched chain (93.85%), the isolates could be identified as a species of Bacillus. According to the experimental results of the API system (API 50CHB & API 20E) the strain was identified as Bacillus subtilis. Numerical texonomy, in which 82 major characters were examined using several species of Bacillus as the standard bacteria, indicated that the strain SH-1 showed 90% similarity to Bacillus subtilis. Thus, the isolated strain SH-1 could be identified as Bacillus subtilis.

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